At present, as a thermal type fluid flow sensor used in an air flow meter provided at an electronically controlled fuel injection apparatus of an internal combustion engine of an automobile or the like for measuring an intake air amount, a main stream is constituted by thermal type ones since a mass air amount can be directly detected thereby.
Among them, attention is paid particularly to a thermal type air flow sensor fabricated by a semiconductor micromachining technology since the sensor can reduce a fabrication cost and can be driven by a low power. As such an air flow sensor, for example, Japanese Unexamined Patent Publication No. 60 (1985)-142268 (Patent Document 1) discloses a technology of arranging a heat generating resistor and a temperature measuring resistor of measuring an air flow on an air cavity formed by partially anisotropically etching an Si substrate. Further, Japanese Unexamined Patent Publication No. Hei7 (1995)-229776 (Patent Document 2) discloses a thermal type air flow meter in consideration of a correction of an intake air amount by a humidity, and according to a technology disclosed by Patent Document 2 described above, a humidity sensor for detecting a humidity is installed separately from a measuring element for a thermal type air flow meter. In a thermal type air flow sensor disclosed in Japanese Unexamined Patent Publication No. Hei10(1998)-197305 (Patent Document 3), an air flow meter and an element of detecting a relative humidity from a change in an electrostatic capacitance are formed on the same substrate. Further, as a method of measuring a humidity, Japanese Unexamined Patent Publication No. Hei7 (1995)-55748 (Patent Document 4) discloses a technology of detecting a humidity by a change in a resistance value of a heated resistor.